Reduction kinetics of the photo-oxidized chlorophyll a11 in chloroplasts measured in the nanosecond range at 837 nm under repetitive flash excitation

The time course of reduction of the photo-oxidized primary donor of Photosystem II (Chl a 11 or P -680) in spinach chloroplasts has been investigated by measuring the absorption changes at 837 nm induced by 3 ns laser flashes. It was found that under repetitive excitation about 50% of the Chl is reduced with a half-life of about 30 ns and 20% with 250 ns. The remaining Chl decays with multiphasic kinetics in the range from about 5 μ s to 350 μ s. Discrepancies in earlier measurements under different conditions and possible explanations for the complex reduction kinetics of Chl a 11 + are discussed.